The present invention relates to a vacuum-operated brake power booster of the type including a movable wall which is sealed relative to the vacuum housing and which is formed by a diaphragm plate and a rolling diaphragm which is, in part, abutted against the diaphragm plate. The booster also includes a piston rod coupled to a brake pedal for the actuation of a control valve connecting one chamber of the brake power booster either with a vacuum or with a higher pressure differential. A control valve piston is axially displaceable within a control valve housing and acts through the intermediary of an interposed reaction element on the end of a push rod. The rolling diaphragm sealingly engages around the control valve housing and is clamped in a peripheral groove of the control valve housing through the intermediary of an edge bead.
In known brake power boosters of the type to which the present invention relates there is, under certain circumstances, a danger of a detachment of the rolling diaphragm from the control valve housing at the edge bead which contributes to considerable degradation of functional safety of the brake booster. This danger occurs, in particular, as a result of blocked pressure in the booster caused by an actuation of the booster without a vacuum and/or with closed non-return valve outlets as well as by the introduction of a pressure above atmospheric during engine misfires. A force component acting in a radial direction is generated in these situations due to the pressure prevailing in the brake power booster housing, which force component causes the annular bead of the rolling diaphragm to detach from the peripheral groove in the control valve housing in which it is received.